Radiotherapy for breast cancer may damage heart
According to a large new study, radiation used to treat and sometimes cure breast cancer can damage the heart; thus leading to later cardiovascular disease and even death. A research team led by Dr. Sarah Darby of the University of Oxford published their findings on March 14 in the New England Journal of Medicine.
The researchers noted that radiotherapy for breast cancer often involves some incidental exposure of the heart to ionizing radiation. The effect of this exposure on the subsequent risk of ischemic heart disease is uncertain. Therefore, the investigators conducted a population-based case–control study of major coronary events (i.e., myocardial infarction (heart attack), coronary revascularization, or death from ischemic heart disease) in 2,168 women who underwent radiotherapy for breast cancer between 1958 and 2001 in Sweden and Denmark. The study group comprised 963 women with major coronary events and 1,205 controls. The patients’ hospital medical records were reviewed. The average radiation doses to the whole heart and to the left anterior descending coronary artery were estimated from each woman’s radiotherapy chart. It should be noted that because is located to the left side of the chest, radiation to the left breast carries a greater exposure risk than that to the right.
The researchers found that the overall average of the doses to the whole heart was 4.9 gray (range: 0.03 to 27.72). (The gray (Gy) is a measurement of the absorbed radiation dose.) The rates of major coronary events increased in a straight line fashion with the average dose to the heart by 7.4% per gray, with no apparent threshold, meaning that any amount of radiation was associated with increased risk. The increase began within the first five years after radiotherapy and continued into the third decade after radiotherapy. The proportional increase in the rate of major coronary events per gray was similar in women with and women without cardiac risk factors at the time of radiotherapy.
The authors concluded that exposure of the heart to ionizing radiation during radiotherapy for breast cancer increases the subsequent rate of ischemic heart disease. The increase is proportional to the average dose to the heart, begins within a few years after exposure, and continues for at least 20 years. Furthermore, women with preexisting cardiac risk factors have greater absolute increases in risk from radiotherapy than other women.
The researchers noted that their results should be comforting to women rather than alarming because their risk of heart attack is so low to begin with and the data allow doctors to factor it into cancer treatment planning.
Take home message:
As with all medical treatments, benefits versus risks must be weighed. For most breast cancer patients, the benefits far outweigh the risks. I consulted with an expert radiologist who informed me that the risk of heart damage for a woman undergoing radiotherapy today is significantly less due to improvements in technology and risk-minimization measures. The women in the study group underwent radiotherapy one to five decades ago. In addition, all women, including those who have undergone radiotherapy to the breast, should engage in cardiovascular health practices that include a healthy diet, exercise, and refraining from smoking.
Reference: New England Journal of Medicine